Telephone system:Cisco PoE hack

Inspired from info at voip-info.org, found it confusing, so I started testing myself..

the stuff tested

• Netgear GS110TP which turned out to be 802.3af type A (power on the data pairs)
• Cisco CP-7940 and CP-7960: known to be pre-standard PoE.
• 22k resistor

what you need to do to build one

• Build an adapter cable that has a regular connector wired type B, and an outlet with the cables crimped on it the same (regular 'extension' cable, but can be very short)
• undo the outlet's cap carefully, keeping the wires in place
• use S-39 on the 'forks' for pin 1 and 3 (white-orange and white-green).
  careful that you have the ordering correct: outlets order pins by color pairs.
  the S-39 is for the forks to quickly get tinned without destroying the insulation
• be sure the leads of the resistor are slightly shortened, so that it will just pop out of the outlet at the back.
• solder it!
• carefully place the cap back with the resistor leads joining the other wires

connecting it

Now, if you connect everything, the phone won't boot. It seems to be a kind of protection.

• leave the phone disconnected
• connect a regular network cable to the switch of your desired length
• connect the adapter's outlet to the cable and wait (at most 5 seconds)
• when the PoE led lights up, plug it in to the CP-79x0 phone's switch socket: it should get power and start the boot sequence

tests

When at first it didn't work, I tried to make a cross cable (at least I think I did, I have to verify the spare pair ordering), but that didn't seem to work either: it triggered power on the switch, but the phone did nothing (probably thanks to a reversed polarity protection diode).

Then, when I plugged in the straight cable without phone, it booted; so I took a gamble and plugged the powered rj45, and it worked.

After testing, the actual network seems to work fine (tested with 3m cable)